Hydraulic lash adjusters are known for use in internal combustion engines to reduce clearance, or lash, between valve train components, and also to maintain engine efficiency, reduce engine noise, and reduce wear in the valve train. Hydraulic lash adjusters operate by transmitting rotational energy of the camshaft through hydraulic fluid trapped in a high pressure volume beneath a piston. During operation of the camshaft, as the length of the valve train components varies due to operational changes, such as thermal stresses, small quantities of hydraulic fluid are permitted to enter or escape from the high pressure volume. As the hydraulic fluid enters or escapes the high pressure volume, the position of the piston is adjusted and, consequently, the effective length of the valve train is adjusted, thus minimizing or eliminating the lash.
During operation of the internal combustion engine, the hydraulic lash adjuster or, more particularly, a fluid reservoir of the hydraulic lash adjuster is provided with a continuous supply of hydraulic fluid. Thus, the hydraulic lash adjuster has a sufficient volume of hydraulic fluid to facilitate the hydraulic length adjustment described above. However, when the internal combustion engine is shut down or during startup of the internal combustion engine, before a sufficient supply of hydraulic fluid is supplied to the hydraulic lash adjuster, the small amount of leakage that occurs during actuation of the hydraulic lash adjuster may deplete the supply of hydraulic fluid before it is effectively replaced. Operation of the hydraulic lash adjuster and valve train during these conditions may result in increased wear and potential damage of the internal combustion engine.
U.S. Pat. No. 4,184,464 to Svihlik teaches an oil recirculation groove formed on the exterior of the plunger of the hydraulic lash adjuster. The oil recirculation groove is in communication with the interior of the plunger through a plunger opening. The oil recirculation groove and plunger opening are positioned axially between the high pressure volume of the hydraulic lash adjuster and an additional groove and passage of the plunger through which oil is supplied to the interior of the plunger. The reduced cross section of the plunger at the circumferential groove may reduce the structural strength of the plunger.
The present disclosure is directed to one or more of the problems set forth above.